Stephen Hawking has set the world of physics back on its heels by reversing his lifetime’s work and a pillar of modern physics claiming that black holes do not exist – saying that the idea of an event horizon, the invisible boundary thought to shroud every black hole --the awesome gravitational pull created by the collapse of a star will be so strong that nothing can break free including light-- is flawed. Hawking proposes that instead of an inescapable event horizon, we should think of an “apparent horizon”.
Hawking says that his revsion requires a new theory that merges gravity with the other fundamental forces of nature. “The correct treatment remains a mystery,” he observed.
Hawking posted his paper, 'Information preservation and weather forecasting for black holes', on the arXiv preprint server. It has yet to pass peer review. The paper was based on a talk he gave via Skype at a meeting at the Kavli Institute for Theoretical Physics in Santa Barbara, California, in August 2013. leading theoretical physicist Joseph Polchinski of the Kavli Institute to comment that “In Einstein’s gravity, the black-hole horizon is not so different from any other part of space. We never see space-time fluctuate in our own neighbourhood: it is just too rare on large scales.”
Raphael Bousso, a theoretical physicist at the University of California, Berkeley, and former student of Hawking's, observes via nature.com, that “The idea that there are no points from which you cannot escape a black hole is in some ways an even more radical and problematic suggestion than the existence of firewalls. But the fact that we’re still discussing such questions 40 years after Hawking’s first papers on black holes and information is testament to their enormous significance."
Hawking's revised theory is an attempt to solve what is known as the black-hole firewall paradox, which has been vexing physicists for almost two years, after it In a thought experiment discovered by theoretical physicist Joseph Polchinski of the Kavli Institute and his colleagues, who asked what would happen to an astronaut unlucky enough to fall into a black hole.
The notion of a firewall obeyed quantum rules, but flouts Einstein’s general theory of relativity. According to that theory, observes Nature.com, "someone in free fall should perceive the laws of physics as being identical everywhere in the Universe — whether they are falling into a black hole or floating in empty intergalactic space. As far as Einstein is concerned, the event horizon should be an unremarkable place."
Hawking proposes a third option in which quantum mechanics and general relativity remain intact, but quantum effects around the black hole cause space-time to fluctuate too wildly for a sharp boundary surface to exist.
The image at the top of the page of NGC 6240 contains new X-ray data from Chandra (shown in red, orange, and yellow) that has been combined with an optical image from the Hubble Space Telescope. In 2002, the discovery of two merging black holes was announced based on Chandra data in this galaxy. The two black holes are a mere 3,000 light years apart and are seen as the bright point-like sources in the middle of the image.
Scientists think these black holes are in such close proximity because they are in the midst of spiraling toward each other -- a process that began about 30 million years ago. It is estimated that the two black holes will eventually drift together and merge into a larger black hole some tens or hundreds of millions of years from now.
The formation of multiple systems of supermassive black holes should be common in the Universe, since many galaxies undergo collisions and mergers with other galaxies, most of which contain supermassive black holes. It is thought that pairs of massive black holes can explain some of the unusual behavior seen by rapidly growing supermassive black holes, such as the distortion and bending seen in the powerful jets they produce. Also, pairs of massive black holes in the process of merging are expected to be the most powerful sources of gravitational waves in the Universe.
Sources: Nature doi:10.1038/nature.2014.14583 and Hawking, S. W. Preprint at http://arxiv.org/abs/1401.5761 (2014)http://arxiv.org/abs/1401.5761 (2014)